The present invention pertains to pressure sensor bags useable in airbag systems used in transportation vehicles and other pressure sensing applications. More particularly, the subject invention pertains to xe2x80x9csmartxe2x80x9d airbag systems which disarm the airbag when an occupant position in a vehicle is unoccupied, or occupied by an infant.
Airbags are now in widespread use, and have been mandated as necessary by numerous governments throughout the world. Recently, it has been discovered that airbag systems conventionally employed may cause serious injury and even death to infants and small children. This has caused many manufacturers to offer xe2x80x9ccutoutxe2x80x9d switches to disarm the passenger seat airbag. If the airbag is disarmed while a passenger of normal height and weight is seated, however, the purpose of providing the airbag is compromised, and injury may result in the event of a collision. Accordingly, so-called xe2x80x9csmartxe2x80x9d airbag systems which can detect the absence of an occupant, or the absence of an occupant of sufficient weight, are being developed.
In xe2x80x9csmartxe2x80x9d systems, deactivation may be achieved through monitoring the pressure exerted on seating components by means of a pressure sensitive switch or device having equivalent function, which is maintained in or associated with a fluid-containing bladder. The fluid-containing bladder is necessary to transmit forces to the pressure sensitive switch from a large seating area, as the passenger may not necessarily be seated in the same position at all times.
The choice of fluid for the fluid-containing bladder is subject to numerous constraints. Water and many other fluids cannot be used because they either change to the solid state at low temperatures and thus become unable to transmit pressure uniformly through the bladder to the pressure sensitive transducer, or exhibit marked change in viscosity over contemplated use temperatures, resulting in great variation in pressure transmission response characteristics. Some fluids which would otherwise be suitable are chemically reactive, or harmful if ingested. Thus, organopolysiloxane fluids, which have the desirable properties of chemical inertness, low solidification point, low toxicity and substantially constant viscosity/temperature profiles have been proposed as pressure transmitting fluids.
While exhibiting desirable properties as fluid pressure transmission media, silicone fluids exhibit several pronounced drawbacks. If a bladder filled with silicone fluid is punctured or ruptured, either as the result of accidental piercing with a sharp object, or due to a collision, the contents will leak from the bladder. This leakage is more than a minor inconvenience. The silicone fluids are very persistent, and can be removed from foam cushions, trim, etc., with difficulty, if at all. Even more important, the silicone fluids, even in exceptionally minor amounts, cause extreme difficulties in refinishing.
Thus, rupture of a pressure transmitting bladder and loss of fluid may require the entire paintable surface areas of the car to be washed with solvent washes and harsh detergents, often by both hand and machine processes, in order that repair areas from a collision may be successfully repainted. These properties of silicone fluids are well documented, and it is for this reason that components employing silicone fluids are often totally banned from automotive assembly plants.
However, the most important drawback to the use of silicone fluids is that in the case of small punctures, the entire fluid may exit the bag, and the pressure sensor will become inoperative, creating a dangerous situation for the passenger.
It would d be desirable to provide a bladder for an airbag system which exhibits the desirable temperature/viscosity profiles of silicone fluids without exhibiting the problems associated with bladders containing silicone fluids.
It has now been surprisingly discovered that soft organopolysiloxane gels provide acceptable pressure-transmitting capability while possessing viscosity/temperature profiles suitable for use in smart airbag systems. Because the gel is distortable but three dimensionally stable, it is able to transmit pressure but is resistant to leakage from the bladder should the latter be punctured or ruptured.